With the constantly developed communication technologies, communication service providers have established many communication machine rooms in urban areas to optimize communication service quality by improving the problems of jammed communication lines, poor signal receiving quality, unstable signal, etc. On the other hand, the communication machine room itself is an important factor in maintaining stable signal quality. Therefore, the communication machine room requires manual maintenance from time to time. People working in the communication machine room must withstand the noises produced in the room by cooling fans provided on the wideband network mainframes or server workstations.
The problem of fan noise has received high attention of the communication service providers, because the noise tends to cause different degrees of discomfort and anxiety to people, make people feel tired easily to reduce work efficiency and suffer from mental and physiological detriment. Conventionally, the noises are only passively suppressed by using sound absorption wool and/or sound insulating boards in the communication machine room or having operators to wear earmuffs to isolate the noises. However, the sound absorption wool, the sound insulating boards, and the earmuffs are only effective in isolating high-frequency noises but not low-frequency noises.
In brief, the conventional ways for passively suppressing the noises in the communication machine room have the following disadvantages:    1. The sound absorption or sound transmission of the building structure and materials has close relation with the noise frequency. Generally speaking, sound absorption materials have effective sound canceling performance for high-frequency noises ranging from 1 KHz to 20 KHz, but are less effective for low-frequency noises lower than 1 KHz.    2. The use of sound absorption wool and sound isolation boards in the communication machine room would only unnecessarily waste the usable space in the room without substantial benefit in suppressing the noises.
It is therefore desirable to overcome the problems and disadvantages in the conventional passive noise suppression in communication machine room.